The present invention relates to a process for producing a carbon heat generator and, more particularly, to such a process permitting manufacture of oxidation resistant carbon heat generator to be used in the air and having free moldability.
A carbon material has excellent heat resistance, thermal impact resistance and corrosion resistance to be expected as a heat generator material. However, the carbon is reacted with gas, such as oxygen, carbon dioxide or steam to be oxidized and consumed. This phenomenon causes the carbon to be a large disturbance in case of using as a heat generator in the air. Accordingly, the conventional carbon heat generator has had a drawback that the carbon can be used only in inactive atmosphere. Thus, recently, various methods for providing oxidation resistance in a carbon material without coating the heat resistant surface with oxidation resistant material have been developed. For example, a process for producing a carbon-ceramic composite material (Japanese Patent Laid-open No. 140,075/1981) filed and assigned to Kyushu Industrial Institute of Technology, in Japan, which provides carbon-ceramic composite material mainly containing as raw material pulverized crude coke. Since this process employs the crude coke as a carbon source, it has such a disadvantage that the process cannot obtain an oxidation resistant carbon material having free moldability due to complicated configuration, such as a coil shape.
To develop a heat resistant heat generator usable in the air with free moldability, the inventors have undertook a study and have started from two concepts, one of which complexes metal compound to form uniform vitreous property when effecting air oxidation in a heat resistant matrix to provide self-recovery for an oxidation resistant film to prevent oxygen from diffusing in the interior and the other of which uses synthetic resin as a pretreated carbon to mold equivalently to a normal plastic molding to uniformly disperse metal compound in synthetic resin.
From the result of the study, the fact that metal compound was uniformly dispersed in synthetic resin, molded in a round-rod shape and carbonized to prevent oxygen from diffusing in the interior thereof due to the construction of uniform vitreous film by the oxidation of the exposed metal compound in the step of oxidizing to consume the carbon on the surface in an oxidative atmosphere so that carbon heat generator thereby stably generates heat without oxidation even in the air has been discovered.
The present invention is devised on the basic of the abovementioned discovery and comprises the steps of uniformly kneading composition, such as synthetic resin exhibiting moldability and high carbon residual yield after calcining, metal compound forming vitreous property in air oxidation and carbon powder to obtain a molding composition, molding the composition in a free shape, carbon pretreating the molded composition in an air oven, and then carbonizing the composition in an inert gas atmosphere. Even if the carbon heat generator thus provided is heated at 800.degree. C. for 30 hours in the air, there are observed almost no external appearance and weight differences before and after the heat generating.